[29178] in North American Network Operators' Group
RE: PMTU-D: remember, your load balancer is broken
daemon@ATHENA.MIT.EDU (Roeland Meyer (E-mail))
Wed Jun 14 12:08:52 2000
Reply-To: <rmeyer@mhsc.com>
From: "Roeland Meyer (E-mail)" <rmeyer@mhsc.com>
To: <Valdis.Kletnieks@vt.edu>, "'Marc Slemko'" <marcs@znep.com>
Cc: <nanog@merit.edu>
Date: Wed, 14 Jun 2000 09:06:52 -0700
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> Valdis.Kletnieks@vt.edu: Wednesday, June 14, 2000 8:07 AM
>
> On Tue, 13 Jun 2000 22:36:08 MDT, Marc Slemko said:
> > It is also a concern that, in my experience, many of the
links with
> > MTUs <1500 are also the links with greater packet loss, etc.
so
> > you really don't want fragmentation on them.
>
> The worst part here is that I suspect that most of these
> links (just on
> sheer numbers of shipped product) are the aformentioned Win98
576-MTU.
I just set my dial PPP ports to MTU=512+40=552, is this wrong?
Where does the MTU=576 number come from?
> I seem to remember that the *original* motivation for
slow-start and
> all that was Van Jacobson's observation that the most common
cause of
> a TCP retransmit was that an *entire* packet had been silently
dropped
> due to queueing congestion, and could thus be treated identical
to
> an ICMP Source Quench.
>
> Has this changed? Has "fragmentation" become a Great Evil,
> rather than
> an annoyance that some links have to deal with?
I'm having some trouble getting full throughput from a GigE pipe.
Even in the 100baseTX/FDX down-stream, I'm not getting full link
utilization (everything on switches, Cat6509 and 3512XLs). I'm
considering increasing MTU sizes to MTU=4096+40, or even larger.
Most of the data transmissions fall into the 5KB-50KB range. The
site can be considered a large portal. What would be the effect
on my upstream? Would it create problems? The only systems that
see the Internet are the web-servers (dual NICs).
